1. Field of the Invention
The present invention relates to an apparatus for controlling a combustion condition in an internal combustion engine having a plurality of combustion cylinders.
2. Description of the Related Art
Known in the prior art is an apparatus for controlling a combustion condition in an internal combustion engine having a plurality of combustion cylinders wherein one or more combustion condition control parameters, such as ignition timing, air-fuel ratio of an air-fuel mixture to be fed into the engine cylinders, or supercharging pressure, are controlled to prevent the generation of knocking in the combustion cylinders when a knocking generated in each engine cylinder is detected by a knocking sensor, such an internal pressure sensor for detecting changes in the internal pressure of the combustion cylinder. For example, Japanese Unexamined Patent Public Disclosure No. 61-215942 discloses a control apparatus comprising internal pressure sensors arranged on combustion cylinders, respectively. In such a kind of apparatus, knocking generated in each combustion cylinder is detected by the corresponding internal pressure sensor, and then ignition timing of each combustion cylinder is controlled in accordance with the output signal from the corresponding internal pressure sensor so as to obtain a critical timing for preventing the generation of knocking. That is, in such a known control apparatus, control of the ignition timing of one combustion cylinder is effected in accordance with the output signal from the corresponding internal pressure sensor.
Such a known control apparatus can detect the generation of knocking with high sensitivity, since the internal pressure sensor can directly detect changes of the internal pressure in the corresponding combustion cylinder. However, in such a known control apparatus, each combustion cylinder requires a corresponding internal pressure sensor and therefore, processing of the signals output from the internal pressure sensors becomes complex and so, it makes the expenses of production of the apparatus costly.